When aqueous solution that contains a guest compound (herein, the guest compound is formed as salts. That is, such as tetra-n-butyl ammonium salt, tetra-iso-amyl ammonium salt, tetra-iso-butyl phosphonium salt, tri-iso-amyl sulfonium salt and etc.). The aqueous solution is cooled, the guest compound is enclosed in a cage-shaped clathrate lattice formed by water molecules, which are host molecules. And the guest compound is crystallized to form a hydrate (liquid clathrate hydrate). The hydrate is generated at equal or higher temperature of 0° C. at atmospheric pressure. The hydrate makes it possible to store the cold heating amount, whose value is several times that of cold water because of the bigger latent heat. The hydrate is composed of fine crystal grains. And the hydrate is suspended in aqueous solution, so that the hydrate exists in a shape of hydrate slurry, which possesses relatively high fluidity. Therefore, such hydrate slurry possesses a preferable characteristic usable for a cold transporting medium for an air-conditioning facility or for an industrial facility to use a cold thermal storage.
Conventionally, cooling aqueous solution that contains a guest compound has generated the above-described hydrate slurry, by means of exchanging heat between the cold medium (such as cold water) and the aqueous solution, by using one set of the heat exchanger. In this case, when the aqueous solution that contains a guest compound is cooled, supercooling occurs. As a result, the hydrate sometimes exists as a form of the aqueous solution at the lower temperature than the temperature, at which the hydrate generates. After the aqueous solution is supercooled in the heat exchanger, supercooling the aqueous solution is canceled on a heat transfer surface in the heat exchanger. At such a procedure, the generated hydrate is easy to be adhered to the heat transfer surface in the heat exchanger. The adhesion degrades the heat transfer performance of the heat exchanger. Furthermore, some case happens that the aqueous solution is supercooled to a great extent in the heat exchanger, and afterwards, supercooling is canceled. In such a case, the hydrate is generated rapidly, so that the viscosity of the hydrate slurry increases, and also the flow resistance and the pressure losses increase. As a result, the corresponding pump power is required to increase. And in the worst case, blocking happens in some part of the heat exchanger. As described above, it causes an unstable system operation to cancel the supercooling of aqueous solution in the heat exchanger.
Additionally, in order for the conventional method to generate the hydrate slurry that possesses a predetermined heat density, the cold water cooled by a refrigerating machine and the aqueous solution that contains a guest compound are transported in some sorts of the heat exchanger. The heat exchanger has a large heat transfer area, such as a plate type one or a multitubular type one. In the conventional method, the mutual materials are exchanged in such a way.
The reason why the above-mentioned disadvantage happens is that it is difficult to generate directly the hydrate slurry that has a predetermined heat density by cooling the aqueous solution, which contains a guest compound by means of exchanging the mutual heat in an evaporator of the refrigerating machine. That is to say, if an attempt is made to generate the hydrate slurry by means of exchanging the mutual heat in the evaporator, the heat resistance increases. Because the viscosity of the hydrate slurry is higher than that of water and the hydrate is apt to adhere to the cooling surface. On the other hand, since the heat transfer area of evaporator is small, it may be that the heat resistance is large, it is very difficult to generate directly the hydrate slurry that has the predetermined heat density.
However, in the above-described conventional apparatus for generating the hydrate slurry, a pump for cold water and a pump for hydrate slurry are required, in addition to a plate type or multitubular type heat exchanger. This requirement invited some sorts of problems such that the equipment cost becomes higher and the energy consumption becomes higher.